A wide variety of processes use counter-current flow reactors to provide for contact between a fluid and a solid. The solid usually comprises a catalytic material on which the fluid reacts to form a product. The processes cover a range of processes, including hydrocarbon conversion, gas treatment, and adsorption for separation.
Counter-current reactors are constructed such that the reactor allows for catalyst, or adsorbent, to flow downward through the reactor, and the gas, or other fluid, flows upward contacting the catalyst. Since catalyst is heavy, and can exert significant force on the reactor internals, the construction has to be with a substantial material, such as thick steel plates. Counter-current reactors provide for continuous processing, with regenerated catalyst entering the reactor and flowing downward though the reactor, to be drawn off. The drawn off catalyst is recycled to a regenerator to refresh the catalyst for reuse. A problem with currently designed counter-current reactors is that the catalyst flows through and is collected in the bottom of the reactor. Significant amounts of the catalyst are bypassed as catalyst sits in the bottom of the reactor waiting to be drawn off for regeneration. In order to reduce the amount of catalyst situated at the bottom of the reactor, the current design is such that a substantial amount of catalyst is retained within the reactor in a non-flowing region. This presents a problem in that the catalyst will eventually be inactivated and is not taken out of the reactor, but creates a dead space where the reactant gas flows and is not processed.
Currently, screens for reactors are directed to reactors that have fluidized beds and where the screens prevent the passage of catalyst, or for radial flow reactors where the stresses on the screens are horizontal pressures. Other screens include high velocity flow processes where the solid particles need to be removed from the flow field. These reactors use different types of screens which are not applicable here.
The design of reactors to overcome these limitations can save significantly on catalyst that is held up in the reactor and does not flow, as well as catalyst that collects at the bottom of the reactor, and is by-passed by the flowing gas. The catalyst is one of the most significant costs associated with hydrocarbon processing, and reductions in amounts of catalyst used, or by-passed can result in significant savings. Improvements can increase the contact between the catalyst and fluid, and can reduce the amount of non-flowing catalyst.